We've heard that ATI is working on an X2 version of Radeon HD 5870 card but the biggest obstacle is the power and how to cool such a card.

We’ve learned that the current TDP for X2 is 376W and that the company is working on this issue, as apparently they will have to slow down the GPUs down by quite a lot to get rid of the heat.

Even if they use downclocked Radeon 5850 cores that run at 725MHz, the power goes down by only 36W (2x170W) to 340W. The hottest card from ATI so far was HD 4870 X2 that had TDP of 286W. To release a Radeon HD 5870 X2 card ATI should go down at least to 300W, especially due to thermal issues, but who knows, maybe ATI will launch 300W+ card.

We might be looking at the dawn of graphics cards with three or even four power connectors, as two might not be enough this time.